The present invention relates to telecommunication networks and, more particularly, to monitoring data transmissions for errors.
In conventional Asynchronous Transfer Mode (ATM) networks, data is transmitted as packets having variable lengths. Packet lengths may range from around 20 bytes to over 65,000 bytes. The data packet is typically transmitted with an error checking code, such as a cyclic redundancy code (CRC). The CRC is conventionally attached to the end of the packet after the user data and is used to detect corruption of the transmitted data packet.
The ATM packets may be transmitted in a network such as a synchronous optical network (SONET). In this case, the packet is broken down into a number of cells having a fixed length. The last cell in the packet normally includes the CRC. A receiver receives the cells and checks for transmission errors using the transmitted CRC. While the receiver is able to determine whether an error occurred in the data transmission, the receiver is unable to localize the error. That is, the receiver cannot identify a particular portion of the packet that contains the erroneous data. Being able to determine where an error occurred in the data transmission often facilitates determining the cause of the error. Additionally, knowing where an error occurred often simplifies the troubleshooting and fixing of any problems in the network.
There exists a need for a system and method that facilitates error checking in a network.
This and other needs are met by the present invention, where a CRC generator generates a CRC for each cell transmitted in a stream of data. The CRC for each cell is then combined with the CRC for other cells in the same packet of data to generate an overall CRC for the packet. The packet CRC may then be checked against an expected value to identify whether an error occurred in the packet transmission.
According to one aspect of the invention, a method for checking a data transmission for errors is provided. The method includes receiving a stream of data comprising a plurality of cells, each cell including a header portion and a data portion, the header portion including a virtual path identifier (VPI) and a virtual channel identifier (VCI). The method also includes stripping the header portion from each of the plurality of cells, generating a cyclic redundancy code (CRC) for the data portion of each of the plurality of cells and calculating an overall CRC for a group of cells having the same VPI and VCI. The method further includes comparing the overall CRC to an expected value.
Another aspect of the present invention provides a system for checking for errors in a packet of data transmitted over a network. The system includes a CRC generator configured to receive a stream of data comprising a plurality of cells and generate a CRC value for each of the plurality of cells. The system also includes a processing device coupled to the CRC generator and configured to receive the CRC value for each of the plurality of cells, generate a packet CRC for a group of cells forming a packet of data, and compare the packet CRC to an expected value.